Well, here goes.

The car was recently tuned for new cams and headwork. When I got the car back it would only hold ~16psi in each gear to redline. It ran fine so I didn't worry about it.

The other day I replaced all my ugly red vaccuum hose with black. Everything is connected in the same way it was before. The only difference in the black hose has a slightly smaller diameter.

With everything connected the same, sometime the boost will bit 21-22psi and hold strong. Sometimes it will continue to climb. I saw it reach 28psi before I let off. The inconsisteancies seemed to be random from what I gathered during my short test drives.

So, I then capped off the other two nipples on the boost solenoid.

Now, if I start out in 1st gear and go WOT through each gear peak boost will hit ~16psi and drop ~2-4psi depending on the gear.

However, if I go easy through 1st and 2nd and go WOT in 3rd, boost will hit 22psi and drop to 21psi but hold strong to redline.

I am using the GM boost solenoid with AEM EMS controlling boost.

It is also noteworthy that the BOV seems to be opening less with the new vaccuum hose. I even loosened the adjustment nut on top of the BOV but it still barely opens.

I am confused. Is it possible the smaller diameter vaccuum hose is the culprit? Can I buy all new vaccuum hose from the dealer and hook it up like stock or does the EMS need a slightly different routing of vaccuum line?

Please help. Thanks in advance.

 

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I would use the same size vac hose that it originally had. You can get all different diameters at autozone or most auto parts stores.

 

I am debating on whether or not I should just go buy stock vaccuum hose and hook it up like it has on the hood vaccuum hose routing diagram.

I just don't know if the AEM will work properly if the line is hooked up like that.

 

Smaller diameter vacuum lines will actually aid in response and performance as this allows for the shortest (or least volume) of space between each reference point, which means less space to fill up with pressure.

I think something else is amiss!

 

Bad solenoid? Bad routing of the vaccuum lines?

Could these be the problem?

 

You keep refering to the "routing" of the lines.

What is different about the way you routed things as opposed to any other setup?

 

You should post your Map... that would help alot in finding out what is the problem.

 

The current routing has the vaccuum hose from connecting all points from the wastegate -> boost solenoid ->BOV ->Intake manifold.

The diagram on the hood shows a closed loop from the wategate ->boost solenoid -> intake pipe. Then another closed loop from BOV -> intake manifold and some other sources near the firewall.

Unless I am reading it wrong that's how it appears to me. Right now the two closed loops are connected. Not sure if that could be a problem or not.

 

I will work on that, the person who tunes it is on vacation right now so it may be hard to get ahold of him.

Does this mean you think the problem is tuning related and not mechanical?

 

Here is what you need to do:

From the turbo outlet:
- Boost solenoid

From the intake manifold:
- BOV

This should help tremendously!